PHOENIX — It’s a dry 108-degree heat this August afternoon, and Tony Valdovinos only prays it gets hotter. The curly-haired field director for Ruben Gallego, a Democrat running in the open House race here, has his reasons.

“We know when it’s hot, we’re the only ones out there,” says Valdovinos, slighting the opposition’s turnout operation as he drives through a wide boulevard en route to an early evening canvass.

In Arizona's 7th District, a generational party brawl has consumed urban Latino politics, pitting a longtime local pol, former Maricopa County Supervisor Mary Rose Wilcox , against Gallego , a former two-term state representative three decades her junior.

The decisive Democratic primary for retiring Rep. Ed Pastor’s seat is Tuesday, but the race has been culminating for weeks thanks to Arizona’s burgeoning permanent early voter list. In the Valley of the Sun’s prohibitively expensive media market, the victor will be decided by direct mail and, most importantly, a month-long get-out-the-vote push in the late summer heat.

In the weeks leading up to the primary, Gallego’s team expressed more confidence they will prevail. They’re probably right: A high-tech ground game has served him well, even in some of the southwest’s oldest barrios.

El Portal in Phoenix. (Bill Clark/CQ Roll Call)

It’s in one of these storied neighborhoods that Wilcox keeps a campaign field office in her restaurant, El Portal, a single-story burnt sienna building within eyeshot of the US Airways Center. The walls are covered in portraits of Cesar Chavez, a handwritten scoreboard for volunteer efforts and a detailed precinct map.

“With the exception of these four precincts, I’ve represented all of this,” Wilcox, 64, says, gesturing toward a northeastern sliver of the yellow map in an interview with CQ Roll Call.

Wilcox started her career more than 30 years ago as the first Latina elected to city council. She went on to succeed Pastor in 1992 as the only Democrat on the Maricopa County Board of Supervisors. She's made many allies in that time — and also a few enemies.

Pastor backs her bid, along with some of the party's Latino voices in Congress, Reps. Luis V. Gutiérrez of Illinois, and Rubén Hinojosa of Texas.

Salvador Reza, 62, an activist who’s known Wilcox for nearly two decades, recalls how she helped local taco cart vendors, Los Taqueros , centralize their commissary so they could continue operating under county health standards — grossing an estimated $4 million a year.

“Gallego is young and inexperienced, but he’s also arrogant,” Reza says, sitting across the table from his preferred candidate. “That’s his problem.”

But here’s the problem for Wilcox: Young Latino voters are more likely to be able to vote than their parents, some of whom are not U.S. citizens. In this majority Hispanic district, the median age is 29, according to the U.S. Census.

“If you don’t get the Spanish speakers and the newcomers, and the community as a whole, you’re not going to win,” Reza adds. “And even Gallego recognizes that: You will not win. You need to win the Mexicano community, or as some people call it, the Latino community, in order to be able to do it.”

The night before, at a party legislative district meeting two miles from the city line in Tolleson, Wilcox lists four reasons why she wants to serve in Congress: immigration reform, jobs and infrastructure, increasing affordable health care options and decreasing violence. The latter is her key point of attack against Gallego, and she's issued mail pieces referencing the Trayvon Martin killing to target the district's small black voting population. She blasts Gallego for getting a "B+" from the National Rifle Association — a sign of approval from the pro-gun group.

For Wilcox, the issue is personal. In 1997, in the aftermath of a heated local debate on a new stadium tax, she was shot by a homeless man in her upper hip. The bullet exploded inside of her leg. A day later, she woke up in a hospital room filled with flowers and light and recalled, “I thought, I either died, or I’m OK.”

In the 17 years since the shooting, Phoenix has changed drastically as one of the fastest-growing cities in the country. But Wilcox's campaign operation had no major political challenges in decades, and therefore no need to change — until this race. Wilcox recalled Pastor advised she upgrade her political operation.

"That was his biggest advice: Don’t change," Wilcox said. "Don’t think because you’re running for Congress, you have to be a different person. You have delivered for the community. You’ve got a style all your own.”

Gallego at Pizza People Pub in Phoenix. (Bill Clark/CQ Roll Call)

It's clear the Gallego campaign is running a vastly different operation. Three miles north of El Portal, Gallego walks into the crowded meeting room at a local labor headquarters wearing white earbuds as he finishes a call.

Gallego has his own advice for the students and early twenty-somethings who have assembled to canvass for him in the mid-week heat: Drink water the night before, and never go inside a home. Once you acclimate to the air conditioning, he explains, you never want to go outside again.

“We know we’re winning. They know we’re winning," Gallego, 34, tells the group, lured by a spread of chips, apples and water. "There’s no way they can out-do us in the field. We all know we’ve been doing this now for three months, and we rarely see them out there. But that doesn’t mean that they’re not going to try. We’re just going to have to keep working harder.”

His aides tout a recent Public Policy Polling survey showing Gallego up 10 points over Wilcox to loud cheers (the poll was sponsored by one of his supporters). The campaign divides the crowd into groups, armed with iPhones and a MiniVAN app that guides them to target likely Democratic voters, house by house. It shows who's already spoken with the person, which candidate they say they're supporting, and if they have been sent a ballot. The results update instantly to headquarters.

“We go where the data tells us to go,” says Valdovinos, 24, a self-described DREAMer. He's inspired by Gallego's personal story: Raised by a single mom, Gallego attended Harvard before enrolling in the Marines. Adrian Valdovinos, 17, rides in the back seat, jumping out to knock on targeted doors while his brother circles the block.

They've borrowed Gallego's ride for this trip. It's an older Toyota Prius with a vertical crack spanning the front windshield.

In this race, even the candidates' vehicles reveal their differences — Wilcox drives a North Star SLS Cadillac with a "MRSROSE" vanity plate.

Later, at a young professionals fundraiser in the trendy Arts District, Gallego sips a beer (Probably Stella, "his favorite," an aide says) and mingles with about 50 people in chic sundresses and unbuttoned collars.

“We are going against an institution — someone who’s been in office for 31 years," he tells them. “We’re running through so much water right now.”

He explains the district needs a field effort because historically it has one of the lowest primary election turnouts in the country. Later, citing the district's young Latino population, Gallego specifies he would want to focus on education and veterans in Congress.

“I don’t think the congressman who has been representing this area has ever really invested in turnout," Gallego says later in an interview. “I would be joining the voices of many other Latino congressman and elected officials who want obviously want to see immigration reform passed. My goal would also be to bring the bigger issues that are also important to the Latino community.”